The discussion came up on the XM-2000 thread on the costs to operate an electric scooter.
Between June 4 and July 4 I used a kill-a-watt meter to gather a full month of power used to charge my two modified e-max scooters. I did no opportunity charging in the field, so in addition to the total mileage and the total KWH at home, I estimated the consumption from 18 charge cycles at work. This was easy because I know the consumption on the return trip and adjusted the consumption at work down a bit to account for going to work being a net downhill ride. So now, the numbers:
Economic Fuel Efficiency:
Cost per KWH residential (Pittsburgh, PA, USA) = $0.11404
Total consumption over one month = 40.25 kwh
Total distance ridden over one month (two scooters) = 703 km = 435 mi
kwh per km = .0572
kwh per mi = .0925
Cost per km = $0.00653
cost per mi = $.0105
Equivalent required fuel economy for gas scooter = 286 miles per gallon (US$3.00/gal)
Equivalent required fuel economy (European) = 0.824 l/100km ($0.792/l)
ENERGY Fuel Efficiency:
(forgive the mixed units...)
Energy content of gasoline = 131 megajoules per gallon or 34.9 MJ per liter
1 kw = 1000 J/sec, so 1KWH = 1000 J/sec * 3600 sec = 3.6 x10^6 J
so, KWH pr gallon = 131 MJ per Gal/3.6MJ per kwh = 36.4 kwh per gallon
scooter uses 0.925 kwh per mi, so:
equiv required energy efficiency (mi per gallon) = 36.4 kwh/gal /0.092 kwh/mi
= 394 miles per gallon = 0.597 l/100 km
Now, some will argue: "but the important thing is CO2 emissions, and the power plant and transmission to the outlet is 25-30% thermally efficient at best, plus about 70% of it (average for US) is generated with coal, which produces somewhat more C02 than gasoline". So, are we back to being no more "clean" than a typical 150 cc scooter? One answer is that this viewpoint is neglecting the energy and CO2 emissions to pump, transport (from the ME), and refine the gasoline - compared to the relatively short train or barge trip from the mine tipple to the power plant, so we may be ahead, even when using the normal coal-rich mix, after all.
Can anyone give a shot at this calculation?
I try to assuage my uncertainty about this situation by buying new-wind-energy offsets - more than enough to cover my total household electric consumption, plus a good bit of what I use at work. Go here: